Vacuum electronic devices are often used in high power and high frequency applications such as a radar transmitter. In vacuum electronic devices the performance parameters tend to deteriorate over time. One mechanism for such performance degradation is deterioration of the cathode which may be associated with the high temperature of operation of thermally assisted cathodes or interaction of the cathode with gases present in the vacuum envelope. If air enters the vacuum envelope surrounding the beam stick as a result of leaks or adsorbed gases are released from the internal surfaces, especially during vacuum electronic device operation when some surfaces become hot, certain gases can react with the elements of the cathode. This degrades the performance of the cathode and the vacuum electronic device's electrical characteristics become irreversibly altered resulting in tube performance deterioration and eventual failure. Other mechanisms of degradation exist for thermal cathodes operating at high temperature. Both diffusion and evaporation contribute to changes in the cathode surface composition which influence cathode performance.